This research component had its origins as part of the Human Genetics Core Resource in the original application for the Indiana Alcohol Research Center (ARC). It is now a separate component which consolidates and supports alcohol challenge studies in twins and families while continuing to rely on the Human Genetics and Database Core Resource for statistical support and zygosity confirmation. During the first years of the ARC, multiple physiological and biobehavioral variables were studied and many were found to have evidence for significant genetic effects. The strongest evidence for genetic control of the acute effects of alcohol was found for electroencephalographic (EEG) changes after alcohol. Variability within dizygotic (DZ) twin-pairs increased markedly after alcohol while the variability within monozygotic (MZ) pairs generally decreased indicating the presence of genetic influences. The relative changes in the within- pair variability for the two zygosities was so great that multiple additive heritability (estimates of the fraction of total variance due to genetic variance) values were found greater than the theoretical upper limit of 1.0. This suggested an upward bias of heritability due to gene interactions. The post-alcohol heritability values were the largest in the alpha-slow (7.6 - 10.0 Hertz) and beta-slow (12.6 - 20.0 Hertz) frequency bands and over the frontal lobes. The Human Genetics Research Component will continue twin studies of the acute effects of alcohol, development of acute tolerance to alcohol and placebo effects on EEG changes and related biobehavioral variables. These twin studies will be carried out both in a clinical research hospital ward in Indianapolis and in the Department of Psychology in Bloomington. Studies comparing family history positive and family history negative young adult males will also be carried out in Bloomington. The results of these studies will be used to develop a protocol designed to detect segregation of single genes in families of twins with extreme responses to alcohol.